Headspace 101: What You Need to Know
Can you list all the serious problems that excessive headspace can cause? For that matter, could you even explain what, exactly, is meant by the term “headspace”? If not, you should watch this instructional video from Brownells. This video defines the term “headspace”, explains why proper headspacing is critically important, and illustrates how headspace gauges work.
Headspace is a measurement from the bolt-face to a point in the chamber. This point of measurement will vary based on the type of cartridge. Improper headspace, either excessive or (conversely) under SAAMI specifications, can cause a variety of problems, many serious.
Problems Caused by Too Much Headspace
Excessive headspace issues can include: light primer strikes, failure to fire, bulged/blown cases, case separations, split shoulders, or unseated primers after firing. Case ruptures caused by excessive headspace can lead to catastrophic failures causing serious injury. That is why headspace is such an important measurement.
Problems Cause by Too Little Headspace
Insufficent (or excessively tight) headspace can prevent the firearm from going into battery, resulting in failure to fire or deformation of the cartridge case. Various feeding and functioning problems can be caused by cases with too little headspace, even if a round can be chambered (with effort).
Similar Posts:
- How to Understand Headspace — What You Need to Know
- Headspace Basics — What You Need to Know
- How and Why to Use Case Gauges for Pistol Cartridges
- UltimateReloader Video Demonstrates Pistol Case Gauges
- Cartridge Headspace — Understanding the Basics
Tags: Brownells, Case Separation, Chambering, Headspace, Video
I never saw a split neck like is shown in the drawing above from excessive headspace. The “neck” splits I have seen from excess headspace were typically partially in the shoulder and traveling up through the neck/shoulder junction up a little into the neck area (but typically not all the way to the mouth of the case). An example: The split I am referring to is one you might see (albeit infrequently) when you fire form cases (like to make 6mm Dasher cases from 6BR brass, etc.) where the chamber you are fire forming the brass in definitely has excess headspace relative to the brass case you are using to fire form.
Editor: Robert, I think you are absolutely right, but this is just an example of the artist who created images for the video not getting things quite right. Like you, we’ve seen the split shoulder issue where the case splits during fire-forming and that migrates up to the neck-shoulder junction and beyond.
There is a good discussion of “Headspace Vs Datum Line” in this Jun ’13 AS forum thread – http://forum.accurateshooter.com/threads/headspace-vs-datum-line.3818442/
One thing that is clear is that the location of the datum for a true wildcat (not just an AI) is pretty much up to the reamer and gauge machinist/shop. Seems very prudent to get your gauge(s) when you get your reamer, i.e., from the same source.
Don’t try to get any insight from the “Headspace (firearms)” wiki. That author seems to think that the headspace for a rimless cartridge is from case base to shoulder-neck junction…NOT.